1. Field of the Invention
The present invention relates to a sheet finisher including a punching unit and more particularly to an image forming system in which the sheet finisher is constructed integrally with or separately from an image forming apparatus.
2. Description of the Background Art
Today, a copier, printer or similar image forming apparatus with a sheet finisher including a punching unit is extensively used. Japanese Patent Laid-Open Publication No. 2001-25995, for example, discloses an image forming apparatus including a punch and a die for punching a sheet, scrap conveying means for conveying the resulting scraps, and a scrap box for storing the scraps. The scrap conveying means is implemented as a screw type conveyor while the scrap box is removably mounted to the outside of the apparatus body. When the scrap box is dismounted from the apparatus body, the scrap conveying means stops being driven, but the apparatus continues its image forming operation. This, according to the above document, not only prevents the scraps from being scattered around the apparatus body, but enhances productivity as to image formation.
However, the problem with the image forming apparatus described above is that the scrap box is mounted on the rear of the apparatus body, as seen from the operation side. The scrap box is therefore difficult to handle although image formation may be continued after the removal of the scrap box.
Japanese Patent Laid-Open Publication No. 7-112861, for example, teaches an image forming apparatus including a container or storing means for storing scraps produced from punched sheets. The container is mounted to or dismounted from the apparatus body via an opening formed in the side wall of the apparatus body. Further, the container is formed of transparent plastics or similar material so as to allow the container to be seen from the outside. The above document additionally proposes an arrangement in which the container is mounted to one side of the apparatus body, so that scraps stored in the container can be dealt with at the outside of the apparatus body. However, the container mounted on the side of the apparatus body needs an exclusive space for the replacement of the container beside the apparatus body. Further, because the container cannot be extended deep into the apparatus body, punching must be performed in the vicinity of the side wall of the apparatus body. It is therefore necessary to limit the direction of sheet conveyance in accordance with the punching position.
Further, Japanese Patent Laid-Open Publication No. 6-155393, for example, proposes an image forming apparatus including a punching mechanism mounted on an openable cover forming part of one side of the apparatus body. Scraps produced by the punching mechanism are stored in a tank removably mounted to the apparatus body. The openable cover, however, needs an exclusive space beside the apparatus body, so that the cover can be opened. It follows that a space broad enough for the tank to be removed is required beside the apparatus body, increasing the overall space to be occupied by the apparatus.
The conventional image forming apparatuses of the type including a sheet finisher with a punching unit have other problems left unsolved, as enumerated below.
(1) When scraps produced from a sheet by the punching unit drop, they should be surely received by a belt including in a scrap conveying unit. To meet this requirement, the belt must be provided with a length great enough to convey the scraps over a distance between, among a plurality of holes, holes at opposite ends, i.e., 80 mm in Japan or 240 mm in Europe. Also, the belt must be positioned beneath the plurality of holes. Further, it is likely that the scraps fail to fully part from the belt due to static electricity.
(2) The scrap box mounted on the rear of the apparatus body is not only difficult to handle, but also problematic when it is dismounted because image formation is continued, i.e., scraps are continuously produced.
(3) To solve the above problem (2), the scrap box or scrap storing means may be mounted on the front of the sheet finisher. This, however, gives rise to another problem that when the scraps conveyed by the scrap conveying means toward the scrap box have fibers appearing on their edges, they are caught by adjoining members and cannot be smoothly or surely introduced into the scrap box.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-155393, 2000-334696 and 2001-2-5995.